No approach is ever more accurate than ‘shut up and calculate’. The ‘Shut up and calculate’ version of Special Relativity, wherein we claim that Minkowski’s equations give us classical lengths but refuse to speculate about how this mysterious transition from Minkowski intervals to classical lengths is achieved, is just as accurate as Special Relativity. It’s just, well, frankly in denial about how the undermining of your intuition of a classical length is not a good reason to stick your fingers in your ears and go “Nah nah nah I’m not listening” with respect to Minkowski’s equations representing physical reality, the way they actually do. You believe this with respect to Special Relativity, and General Relativity, and every other “shut up and calculate” version of every physical theory from chemistry to nuclear engineering—that there’s no reason to shut up with respect to these other disciplines. I just believe it with respect to quantum mechanics too.
there’s no reason to shut up with respect to these other disciplines. I just believe it with respect to quantum mechanics too.
So do I, and have stated as much. Not sure where the misunderstanding is coming from.
You ought to, however, agree that QM is special: no other physical model has several dozens of interpretations, seriously discussed by physicists and philosophers alike. This is an undisputed experimental fact (about humans, not about QM).
What is so special about QM that inspires interpretations? Many other scientific models are just as counter-intuitive, yet there is little arguing about the underlying meaning of equations in General Relativity (not anymore, anyway) or in any other model. To use your own meta-trick, what is it so special about the Quantum theory (not about the quantum reality, if you believe in such) that inspires people to search for interpretations? Maybe if we answer this reasonably easy cognitive science question first, we can then proceed to productively discuss the merits of various interpretations.
You ought to, however, agree that QM is special: no other physical model has several dozens of interpretations, seriously discussed by physicists and philosophers alike. This is an undisputed experimental fact (about humans, not about QM).
Perhaps you mean the sheer quantity is so great. But there have been, an are, disputes about classical pysyics and relativity. Some of them have been resolved by just beiieving the theory and abandoning contrary intuitions. At one time, atoms were dismissed as a “mere calculational device”. Sound familiar?
Sure, every new theory is like that initially. But it only takes a short time for the experts to integrate the new weird ideas, like relative spacetime, or event horizons, or what have you. There is no agreement among the experts about the ontology of QM (beyond the undisputed assertion that head-in-the-sand “shut up and calculate” works just fine), and it’s been an unusually long time. Most agree that the wave function is, in some sense, “real”, but that’s as far as it goes. So the difference is qualitative, not just quantitative. Simply “trusting the SE” gives you nothing useful, as far as the measurement is concerned.
It doesn’t work “fine”, or at all, as an interpretation. It’s silent as to what it means.
There is no agreement among the experts about the ontology of QM (b
There are slowly emerging themes, such as the uselessness of trying to recover classical physics at the fundamental level, and the importance of decoherence.
Simply “trusting the SE” gives you nothing useful, as far as the measurement is concerned.
I don’t see what you mean by that. An interpretation that says “trust the SE” (I suppose you mean “reify the evolution of the WF according to the SE”) won’t give you anything results-wise, because its an interpretation
Most agree that the wave function is, in some sense, “real”, but that’s as far as it goes
Yeah. Note also that if you are observing a probability distribution, that doesn’t imply that something computed the probability density function. E.g. if you observe random dots positions of which follow Gaussian distribution, that could be count of heads in a long string of coin tosses rather than Universe Machine really squaring some real number, negating result, and calculating an exponent.
There’s certainly one obvious explanation which occurs to me. There being a copy of you in another universe seems more counterintuitive than needing to give up on measuring distances, so it’s getting more like the backlash and excuses that natural selection got, or that was wielded to preserve vitalism, as opposed to the case of Special Relativity. Also the simple answer seems to have been very hard to think of due to some wrong turns taken at the beginning, which would require a more complex account of human cognitive difficulty. But either way it doesn’t seem at all unnatural compared to backlash against the old Earth, natural selection, or other things that somebody thought was counterintuitive.
You need to realize that the “simple answer” isn’t so simple- no one has been able to use the axioms for many worlds to make an actual calculation of anything. By kicking away the Born amplitudes, they’ve kicked away the entire predictive structure of the theory. You are advocating that physicists give up the ability to make predictions!
Its even worse when you go to quantum field theories and try to make many worlds work- the bulk of the amplitude will be centered on “world’s” with undefined particle number.
On a related note, in MWI there is an uncountable number of worlds with the cat is in various stages of decay once the box is open. Is that weird or what.
You’re asking exactly what it is about a theory which speaks of unobserved cats as dwelling in existential limbo, that would inspire people to seek alternatives?
Read Elizier’s sequence on quantum mechanics. The cat does not collapse into a dead or alive state, the cat is dead, and another cat is alive. One of the many worlds has a dead cat, another has a live cat.
You have to remember that ‘interpretations’ of quantum mechanics are actually reformulations of quantum mechanics. Just as classical mechanics can be described by Newton’s laws, or one of several action principals (Hamilton/Jacobi,Maupertuis’ principle,etc), quantum mechanics has many formulations, each with their own axioms- there is nothing unique about quantum in this sense.
What IS unique about quantum mechanics is that so many interpretations are incomplete. Copenhagen is circular (to make sense of the measurement axiom, you need correspondence principle axiom, but classical needs to be a limit of quantum mechanical.) The measurement problem is a formal problem with the axioms of the theory.
Of course, many worlds is in an even worse position. No one has yet to effectively derive the Born amplitudes which means the interpretation is broken, there is no recipe to extract information about measurements from the theory.
Bohm might be an actual complete interpretation but its nearly impossible to extend the formalism to quantum field theories, Consistent histories is where I put my money- the homogenous history class operator seems potentially like the missing piece.
Consistent histories is where I put my money- the homogenous history class operator seems potentially like the missing piece.
Hmm, I could never make sense of the formalism of CH (it seems to rely on time-ordering and density matrices, neither of which inspire confidence, given that one expects a relativistically invariant evolution of a pure state), and the popular write-ups sound like advocacy.
Why would you expect relativistic invariance? The Schroedinger equation isn’t even Galilean invariant ( the mass comes through as a central charge, the probabilities are Galilean but not lorentz invariant)
The best reference for consistent histories is Bob Griffith’s excellent text (not to be confused with the other Griffiths)
Because I would expect a model that has a hope in hell of getting deeper toward the measurement problem than “shut up and calculate” to give a relativistically invariant account of the EPR, and because I expect such a model to be built on top of some form of QFT (as I mentioned in another reply, the number of particles is not conserved during the measurement, so the Hilbert space doesn’t cut it, you need something like a Fock space, second quantization etc.).
But the only way you are going to get relativistic invariance is to throw out the Schroedinger equation. The hope is that an interpretation makes it easier to move to QFT, NOT that a given interpretation will be Lorentz invariant (which is impossible, given the Schreodinger equation).
So far none of the interpretations of quantum are built on top of QFT, mostly because QFT isn’t yet formalized, its a hodge podge of heuristics that gets the right answer. The handful of axiomatic field theories don’t actually describe physical systems. Some people have a pipe dream that finding better quantum axioms will point the way toward better QFT axioms, but I’m not in that camp.
The SE should be a non-relativistic limit of whatever model is the next step. Not sure if it requires a formalization of QFT, it just needs to make decent predictions. Physicists are not overly picky. As long as it’s reasonably self-consistent. Or not even. As long as it helps you calculate something new and interesting unambiguously.
QFT IS the obvious next-step, but the reason people play with standard quantum formulations instead of trying to work in the context of QFT and ‘push the interpretation down’ is that QFT isn’t yet on firm footing.
Hmmm… apparently making QM play nice with Special Relativity isn’t quite as simple as using the Dirac equation instead of the Schrodinger equation, because the Dirac equation has negative energy solutions, and making it impossible for electrons to “decay” into these negative energy states requires kludges.
Quantized wave function solves the negative energy problem, at the expense of introducing a bunch of infinities, some of which are easier to work around (renormalize) than others. For example, there is no way to usefully quantize gravitational field.
This isn’t quite true. What solves the problem isn’t quantizing wave functions, its insisting that positive energy propagate forward in time- i.e. picking the Feynman propagator (instead of the retarded or advanced propagator, etc) that solves the problem. You still have to make a division between the positive energy and negative energy pole in the propagator (unfortunately, all observers can’t agree on which states have positive and what states have negative energy, which is the basis of the Unruh effect- two observers accelerating relative two each other cannot agree on particle number).
Also, its a misconception that you can’t simply quantize the gravitational field. If you treat GR as an effective theory you can make calculations of arbitrary accuracy with a finite number of measured parameters, with just canonical quantization. The standard model is ALSO not a renormalizable field theory (not since the addition of neutrino masses). Weinberg has recently tried to make the argument that maybe GR + canonical quantization (i.e. gravity is asymptotically safe)
Thanks for the corrections, my area is mostly classical GR, not Standard Model physics. And a good point on the Unruh effect. As for quantizing GR, note the “useful” disclaimer. I am deeply suspicious of any technique that treats GR as an effective field theory on some background spacetime, as it throws away the whole reason why GR is unlike any other field theory. Weinberg is especially prone to to doing that, so, while I respect anything he does in HEP, I don’t put much stock into his GR-related efforts. If anything, I expect the progress to come from the entropic gravity crowd, with nothing to quantize.
When I worked in physics I did perturbative QCD stuff in graduate school and then effective theories for medium energy scattering, and finally axiomatic quantum field theories as a postdoc before I left physics for a field with actual employment opportunities (statistics/big data stuff).
But why shouldn’t GR be treated as just another field theory? It certainly has the structure of a field theory. Feynman and then Weinberg managed to show that GR is THE self-consistent, massless spin-2 field theory- so to that extent it IS just another field theory.
Treating GR as an effective theory works. I doubt that the theory is asymptotically safe, but for an effective theory, who cares? Why should we treat the matter part of the action any differently than we treat the spacetime piece of the action?
But why shouldn’t GR be treated as just another field theory? It certainly has the structure of a field theory.
That’s a separate discussion, but let me just note that the action would have to be summed not just over all paths (in which spacetime?), but also over all possible (and maybe impossible) topologies, as well.
No approach is ever more accurate than ‘shut up and calculate’. The ‘Shut up and calculate’ version of Special Relativity, wherein we claim that Minkowski’s equations give us classical lengths but refuse to speculate about how this mysterious transition from Minkowski intervals to classical lengths is achieved, is just as accurate as Special Relativity. It’s just, well, frankly in denial about how the undermining of your intuition of a classical length is not a good reason to stick your fingers in your ears and go “Nah nah nah I’m not listening” with respect to Minkowski’s equations representing physical reality, the way they actually do. You believe this with respect to Special Relativity, and General Relativity, and every other “shut up and calculate” version of every physical theory from chemistry to nuclear engineering—that there’s no reason to shut up with respect to these other disciplines. I just believe it with respect to quantum mechanics too.
So do I, and have stated as much. Not sure where the misunderstanding is coming from.
You ought to, however, agree that QM is special: no other physical model has several dozens of interpretations, seriously discussed by physicists and philosophers alike. This is an undisputed experimental fact (about humans, not about QM).
What is so special about QM that inspires interpretations? Many other scientific models are just as counter-intuitive, yet there is little arguing about the underlying meaning of equations in General Relativity (not anymore, anyway) or in any other model. To use your own meta-trick, what is it so special about the Quantum theory (not about the quantum reality, if you believe in such) that inspires people to search for interpretations? Maybe if we answer this reasonably easy cognitive science question first, we can then proceed to productively discuss the merits of various interpretations.
Perhaps you mean the sheer quantity is so great. But there have been, an are, disputes about classical pysyics and relativity. Some of them have been resolved by just beiieving the theory and abandoning contrary intuitions. At one time, atoms were dismissed as a “mere calculational device”. Sound familiar?
Sure, every new theory is like that initially. But it only takes a short time for the experts to integrate the new weird ideas, like relative spacetime, or event horizons, or what have you. There is no agreement among the experts about the ontology of QM (beyond the undisputed assertion that head-in-the-sand “shut up and calculate” works just fine), and it’s been an unusually long time. Most agree that the wave function is, in some sense, “real”, but that’s as far as it goes. So the difference is qualitative, not just quantitative. Simply “trusting the SE” gives you nothing useful, as far as the measurement is concerned.
It doesn’t work “fine”, or at all, as an interpretation. It’s silent as to what it means.
There are slowly emerging themes, such as the uselessness of trying to recover classical physics at the fundamental level, and the importance of decoherence.
I don’t see what you mean by that. An interpretation that says “trust the SE” (I suppose you mean “reify the evolution of the WF according to the SE”) won’t give you anything results-wise, because its an interpretation
Uh, no. It’s not an interpretation (i.e. “explanation”), it’s an explicit refusal to interpret the laws.
Anyway, time to disengage, we are not converging.
Yeah. Note also that if you are observing a probability distribution, that doesn’t imply that something computed the probability density function. E.g. if you observe random dots positions of which follow Gaussian distribution, that could be count of heads in a long string of coin tosses rather than Universe Machine really squaring some real number, negating result, and calculating an exponent.
There’s certainly one obvious explanation which occurs to me. There being a copy of you in another universe seems more counterintuitive than needing to give up on measuring distances, so it’s getting more like the backlash and excuses that natural selection got, or that was wielded to preserve vitalism, as opposed to the case of Special Relativity. Also the simple answer seems to have been very hard to think of due to some wrong turns taken at the beginning, which would require a more complex account of human cognitive difficulty. But either way it doesn’t seem at all unnatural compared to backlash against the old Earth, natural selection, or other things that somebody thought was counterintuitive.
You need to realize that the “simple answer” isn’t so simple- no one has been able to use the axioms for many worlds to make an actual calculation of anything. By kicking away the Born amplitudes, they’ve kicked away the entire predictive structure of the theory. You are advocating that physicists give up the ability to make predictions!
Its even worse when you go to quantum field theories and try to make many worlds work- the bulk of the amplitude will be centered on “world’s” with undefined particle number.
You mean that “simple answer” that still can’t make predictions?
Cat neither dead nor alive until you open the box?
Yeah, that’s pretty special, but why?
On a related note, in MWI there is an uncountable number of worlds with the cat is in various stages of decay once the box is open. Is that weird or what.
You’re asking exactly what it is about a theory which speaks of unobserved cats as dwelling in existential limbo, that would inspire people to seek alternatives?
Read Elizier’s sequence on quantum mechanics. The cat does not collapse into a dead or alive state, the cat is dead, and another cat is alive. One of the many worlds has a dead cat, another has a live cat.
Read this thread where that idea is shown not to be a “slam dunk”.
You have to remember that ‘interpretations’ of quantum mechanics are actually reformulations of quantum mechanics. Just as classical mechanics can be described by Newton’s laws, or one of several action principals (Hamilton/Jacobi,Maupertuis’ principle,etc), quantum mechanics has many formulations, each with their own axioms- there is nothing unique about quantum in this sense.
What IS unique about quantum mechanics is that so many interpretations are incomplete. Copenhagen is circular (to make sense of the measurement axiom, you need correspondence principle axiom, but classical needs to be a limit of quantum mechanical.) The measurement problem is a formal problem with the axioms of the theory.
Of course, many worlds is in an even worse position. No one has yet to effectively derive the Born amplitudes which means the interpretation is broken, there is no recipe to extract information about measurements from the theory.
Bohm might be an actual complete interpretation but its nearly impossible to extend the formalism to quantum field theories, Consistent histories is where I put my money- the homogenous history class operator seems potentially like the missing piece.
Hmm, I could never make sense of the formalism of CH (it seems to rely on time-ordering and density matrices, neither of which inspire confidence, given that one expects a relativistically invariant evolution of a pure state), and the popular write-ups sound like advocacy.
Why would you expect relativistic invariance? The Schroedinger equation isn’t even Galilean invariant ( the mass comes through as a central charge, the probabilities are Galilean but not lorentz invariant)
The best reference for consistent histories is Bob Griffith’s excellent text (not to be confused with the other Griffiths)
Because I would expect a model that has a hope in hell of getting deeper toward the measurement problem than “shut up and calculate” to give a relativistically invariant account of the EPR, and because I expect such a model to be built on top of some form of QFT (as I mentioned in another reply, the number of particles is not conserved during the measurement, so the Hilbert space doesn’t cut it, you need something like a Fock space, second quantization etc.).
But the only way you are going to get relativistic invariance is to throw out the Schroedinger equation. The hope is that an interpretation makes it easier to move to QFT, NOT that a given interpretation will be Lorentz invariant (which is impossible, given the Schreodinger equation).
So far none of the interpretations of quantum are built on top of QFT, mostly because QFT isn’t yet formalized, its a hodge podge of heuristics that gets the right answer. The handful of axiomatic field theories don’t actually describe physical systems. Some people have a pipe dream that finding better quantum axioms will point the way toward better QFT axioms, but I’m not in that camp.
The SE should be a non-relativistic limit of whatever model is the next step. Not sure if it requires a formalization of QFT, it just needs to make decent predictions. Physicists are not overly picky. As long as it’s reasonably self-consistent. Or not even. As long as it helps you calculate something new and interesting unambiguously.
QFT IS the obvious next-step, but the reason people play with standard quantum formulations instead of trying to work in the context of QFT and ‘push the interpretation down’ is that QFT isn’t yet on firm footing.
::does some reading on Wikipedia::
Hmmm… apparently making QM play nice with Special Relativity isn’t quite as simple as using the Dirac equation instead of the Schrodinger equation, because the Dirac equation has negative energy solutions, and making it impossible for electrons to “decay” into these negative energy states requires kludges.
(Why is it that, the more I learn about QM, the more it seems like one kludge after another?)
Quantized wave function solves the negative energy problem, at the expense of introducing a bunch of infinities, some of which are easier to work around (renormalize) than others. For example, there is no way to usefully quantize gravitational field.
This isn’t quite true. What solves the problem isn’t quantizing wave functions, its insisting that positive energy propagate forward in time- i.e. picking the Feynman propagator (instead of the retarded or advanced propagator, etc) that solves the problem. You still have to make a division between the positive energy and negative energy pole in the propagator (unfortunately, all observers can’t agree on which states have positive and what states have negative energy, which is the basis of the Unruh effect- two observers accelerating relative two each other cannot agree on particle number).
Also, its a misconception that you can’t simply quantize the gravitational field. If you treat GR as an effective theory you can make calculations of arbitrary accuracy with a finite number of measured parameters, with just canonical quantization. The standard model is ALSO not a renormalizable field theory (not since the addition of neutrino masses). Weinberg has recently tried to make the argument that maybe GR + canonical quantization (i.e. gravity is asymptotically safe)
Thanks for the corrections, my area is mostly classical GR, not Standard Model physics. And a good point on the Unruh effect. As for quantizing GR, note the “useful” disclaimer. I am deeply suspicious of any technique that treats GR as an effective field theory on some background spacetime, as it throws away the whole reason why GR is unlike any other field theory. Weinberg is especially prone to to doing that, so, while I respect anything he does in HEP, I don’t put much stock into his GR-related efforts. If anything, I expect the progress to come from the entropic gravity crowd, with nothing to quantize.
When I worked in physics I did perturbative QCD stuff in graduate school and then effective theories for medium energy scattering, and finally axiomatic quantum field theories as a postdoc before I left physics for a field with actual employment opportunities (statistics/big data stuff).
But why shouldn’t GR be treated as just another field theory? It certainly has the structure of a field theory. Feynman and then Weinberg managed to show that GR is THE self-consistent, massless spin-2 field theory- so to that extent it IS just another field theory.
Treating GR as an effective theory works. I doubt that the theory is asymptotically safe, but for an effective theory, who cares? Why should we treat the matter part of the action any differently than we treat the spacetime piece of the action?
That’s a separate discussion, but let me just note that the action would have to be summed not just over all paths (in which spacetime?), but also over all possible (and maybe impossible) topologies, as well.